October 19, 2014

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Borderless Sea

image by Dmitry Makolkin, Moscow, Russia

Mare Australe is a peculiar sea. It doesn't have any broad expanse of lava like other maria, rather it has lava fillings within craters and in low spaces between craters. Only a few of the craters have names, including Harlan cut in half at the left margin. [This might be appropriate because Harlan is only half of the name of the honored person. Harlan Smith was a much-liked American astronomer who died in 1991. But because there was already a Smith on the Moon the IAU broke its custom by using his first name; not only that, the crater already had a designation, Marinus D, so a second custom was vanquished by renaming a lettered crater. Sorry for the aside.] The large dark-floored crater to the right of Harlan is 79 km wide Oken, an Endymion look-alike. And the 150 km wide dark mass closer to the limb is Lyot. Do you notice that the left/north part of the floor is darker than the right/south? That is evidence for two different ages - young lavas tend to be dark and then they are lightened by rays - or two different compositions with different brightnesses. A glance at LRO Quickmap shows that the first interpretation is correct - the lighter-hued lavas to the right are more heavily pitted with craters. Different periods of volcanism is a pattern for Australe, notice the two very dark crater floors near the center, and lighter floors in other places. Although there has been some crater counting to estimate lava ages, and some earlier multispectral studies, Mare Australe - like most farside maria - has not yet received a comprehensive new investigation that LRO and other modern data sets permit.

Chuck Wood

Technical Details
TAL-250K 250mm F/8.5, Barlow 1.5x, filter Astronomik IR Pro 742nm. Camera: Point Grey Blackfly BFLY-PGE-13E4M. 384 frames of 2400 stacked in Autostakkert2, Lucy-Richardson deconvolution, levels, gamma, unsharp masks.

Related Links
21st Century Atlas charts L3 & B3.
Dmitry's Moon gallery
Australe: A Mare on the Edge

Yesterday's LPOD: Big Plain

Tomorrow's LPOD: Big Cooling Cracks


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